1. Field of the Invention
The present invention relates to a spindle drive for adjusting structural components of a motor vehicle seat which are movable relative to one another and, more particularly, to a spindle drive having an encased spindle nut with break-free moment reducing opposite end collars.
2. Description of the Prior Art
Spindle drives for movably adjusting structural components of a motor vehicle seat relative to one another, are known, for example, from prior art patent documents WO 98/26951 and JP 8156660-A, which include a threaded spindle, a casing and a spindle nut supported in the casing and threadably coupled and running on the threaded spindle. In such spindle drive having an encased spindle nut, a soft form-fitting bearing is provided between the casing and spindle nut and surrounds the circumference of the spindle nut so as to ensure smoothness of running of the spindle nut on the spindle and provide a tolerance compensation for accommodating oblique positions arising between the casing and spindle.
One problem of a spindle drive with an encased spindle nut is that the spindle drive operates against end stops where a strong wedging occurs between the face of the end stop and the parallel front face of the casing. For disengagement of the wedging between the respective faces the generation of a large break-free moment is required for which a suitable motor gearing unit must be provided to operate the spindle drive. This required break-free moment provided by the motor gearing unit is multiple times greater than the torque required for the normal adjustment operation of the spindle drive. Thus, in order for the motor gearing unit to be able to provide the required break-free moment it must be overdesigned and overdimensioned with respect to the normal operational torque of the spindle drive.
In the case of a spindle drive with a non-encased spindle nut, the aforementioned problem is solved by providing the end stops projecting radially from the spindle and by providing corresponding protrusions axially projecting on the front faces of the spindle nut. At the end of the adjustment path the end stops abut the protrusions without contacting the front faces of the spindle nut. Through this arrangement constraints between the threads of the threaded spindle and spindle nut are avoided. Such or similar solutions are known, for example, from prior art patent documents DE 32 38 944 A1, DE 40 19 482 C2 and U.S. Pat. No. 4,858,481.
A need exists for an innovation that will solve the aforementioned wedging problem that occurs in the case of spindle drives with encased spindle nuts. An innovation particularly desired is one that will exploit the presence of the elastic form-fitting bearing, provided in any event between the spindle nut and casing, so as to reduce or avoid entirely the break-free moment requirement.
The present invention avoids and thus solves the aforementioned wedging problem in the case of a spindle drive with an encased spindle nut by introducing at least one coaxial end collar on at least one of the respective opposite faces of the spindle nut, the coaxial collar radially and threadably extending about the threaded spindle and also radially spaced from and extending through an opening in a corresponding one of opposite end walls of the casing so as to provide radial play relative to the casing end wall and define a surface against which a corresponding one of the end stops at one end of the adjustment path can abut such that a wedging of the end stop with the casing end wall is avoided.
The present invention also introduces a plurality of elastic elements which are disposed between the exterior of the spindle nut and interior of the casing and form-fittingly elastically supports the spindle nut in the casing at a plurality of predetermined locations on the circumference of the spindle nut. By such arrangement, the spindle nut, in response to the effect of a torque produced by the rotation of the spindle, can twist slightly against a resiliency force of the elastic elements in the casing. Such a torque acts or is applied onto the spindle nut inter alia during run-up and abutting of the end surface of the coaxial collar onto and against the associated one of the end stops. A prestressing effect is thereby applied onto the elastic elements by the spindle nut which counteracts any jamming of the threads of the spindle nut with the threads of the spindle. Due to such prestressing effect, the spindle nut is rotated back into its normal position when the application of torque by the rotation of the spindle ceases and so the prestressing effect at least reduces, if not eliminates, the requirement for a break-free moment, as in the case of the prior art, since the prestressing effect acts in the same direction.
As a consequence, a motor gearing unit of the spindle drive can be provided or designed for the required operational torque and thus can be dimensioned smaller in comparison to the prior art unit. This constitutes a substantial advantage since weight and space savings play a significant role in motor vehicle construction. Apart from this advantage, the advantages known from the prior art of the elastic bearing supporting the spindle nut in the casing are retained since the spindle nut, due to the radial play between casing opening and the coaxial end collar, can still tilt axially as before.
More particularly, the casing and spindle nut are advantageously provided with rectangular configurations in cross section such that circumferentially spaced corners on the spindle nut have notches defined therein for form-fitting reception of the respective elastic elements which are confined in the notches by the inner edges of associated circumferentially spaced corners on the casing which are located diametrically opposite the notches on the corners of the spindle nut. Due to this arrangement, the spindle nut is retained on its circumference resiliently and form-fittingly by the elastic elements on all sides on the casing walls and the reset force of the elastic elements is even greater, even though the elastic elements do not completely envelop the spindle nut in contrast to the elastic bearing of the prior art.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.